Premenstrual dysphoric disorder (PMDD), a severe variant of premenstrual syndrome, affects 2-5% of women in their reproductive years, with decreases in quality of life comparable to those observed in major depressive disorder (Epperson et al., 2012; Halbreich et al., 2003; Wittchen et al., 2002). The disorder is nonetheless understudied, and treatment of PMDD is hindered by a lack of knowledge regarding its neurobiological basis. Affective symptoms, such as irritability/anger, depression, mood swings, anxiety, which appear in the luteal phase, suggest that problems with emotion regulation may contribute to the disorder, but we are aware of no study of emotion regulation in women with PMDD. We hypothesize that dysfunction in the neural circuitry that mediates emotion regulation is an important contributor to the affective symptoms of PMDD. The primary objective of this project is to test this idea, using functional magnetic resonance imaging (fMRI), in women with PMDD and comparison participants without the disorder. Two groups of women (n=18 per group) will undergo fMRI while performing validated tasks that involve presentation of emotionally evocative images, and the intentional and incidental regulation of negative emotional response. Testing will be done during the late luteal phase of the menstrual cycle, when PMDD symptoms occur, and the follicular phase. Success in this project will help clarify the etiology of the symptoms of PMDD, and provide biomarkers for assessing behavioral and pharmacological interventions to ameliorate this disorder.